Compressed feedback format for WLAN

ABSTRACT

In a method for transmitting channel feedback data from a receiver to a transmitter, channel data for a plurality of orthogonal frequency division multiplexing (OFDM) tones for one or more spatial streams corresponding to a communication channel is determined. A plurality of angle values associated with the one or more spatial streams and one or more OFDM tones is determined. For each of the one or more spatial streams, a per-tone signal to noise ratio (PT-SNR) associated with one or more OFDM tones is determined, and an average signal to noise ratio (avg-SNR) is determined by averaging the signal to noise ratio (SNR) values. A feedback report is generated to include at least i) the plurality of angle values, ii) the PT-SNRs, and iii) the avg-SNR. The feedback report is included in a data unit to be transmitted from the receiver to the transmitter.

CROSS-REFERENCES TO RELATED APPLICATIONS

This disclosure claims the benefit of U.S. Provisional PatentApplication No. 61/389,635, filed on Oct. 4, 2010, the disclosure ofwhich is hereby incorporated by reference herein in its entirety.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to communication networks and,more particularly, to frame format for compressed feedback forbeamforming applications.

BACKGROUND

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent it is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

Development of wireless local area network (WLAN) standards such as theInstitute for Electrical and Electronics Engineers (IEEE) 802.11a,802.11b, 802.11g, and 802.11n Standards, has improved single-user peakdata throughput. For example, the IEEE 802.11b Standard specifies asingle-user peak throughput of 11 megabits per second (Mbps), the IEEE802.11a and 802.11g Standards specify a single-user peak throughput of54 Mbps, and the IEEE 802.11n Standard specifies a single-user peakthroughput of 600 Mbps. Work has begun on a new standard, IEEE 802.11ac,that promises to provide even greater throughput.

SUMMARY

In one embodiment, a method for transmitting channel feedback data froma receiver to a transmitter includes determining channel data for aplurality of orthogonal frequency division multiplexing (OFDM) tones forone or more spatial or space-time streams corresponding to thecommunication channel. The method also includes determining a compressedform of the channel data including determining a plurality of anglevalues associated with i) the one or more spatial streams or space-timeand ii) one or more OFDM tones of the plurality of OFDM tones. Themethod further includes, for each of the one or more spatial orspace-time streams, i) determining a per-tone signal to noise ratio(PT-SNR) associated with one or more OFDM tones of the plurality of OFDMtones, and ii) determining an average signal to noise ratio (avg-SNR) byaveraging signal to noise ratio (SNR) values associated with one or moreOFDM tones of the plurality of OFDM tones. The method further yetincludes generating a feedback report to include at least i) theplurality of angle values associated with the one or more spatial orspace-time streams and the one or more OFDM tones, ii) the PT-SNRscorresponding to the one or more spatial or space-time streams and theone or more OFDM tones, and iii) the avg-SNR corresponding to the one ormore spatial or space-time streams. The method further still includesincluding the feedback report in a data unit to be transmitted from thereceiver to the transmitter.

In another embodiment, an apparatus includes a network interfaceconfigured to determine channel data for a plurality of orthogonalfrequency division multiplexing (OFDM) tones for each of one or morespatial or space-time streams corresponding to the communicationchannel. The network interface is also configured to determine acompressed form of the channel data including determining a plurality ofangle values associated with i) the one or more spatial streams orspace-time and ii) one or more OFDM tones of the plurality of OFDMtones. The network interface is further configured to, for each of theone or more spatial or space-time streams, i) determine a per-tonesignal to noise ratio (PT-SNR) associated with one or more OFDM tones ofthe plurality of OFDM tones, and ii) determine an average signal tonoise ratio (avg-SNR) associated with one or more OFDM tone of theplurality of OFDM tones. The network interface is further yet configuredto generate a feedback report to include at least i) the plurality ofangle values corresponding to the one or more spatial or space-timestreams and the one or more OFDM tones, ii) the PT-SNRs corresponding tothe one or more spatial or space-time streams and the one or more OFDMtones, and iii) the avg-SNR corresponding to the one or more spatial orspace-time streams. The network interface is further still configured toinclude the feedback report in a data unit to be transmitted for thereceiver to the transmitter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an example wireless communication networkin which channel data feedback is utilized, according to an embodiment.

FIG. 2 is a diagram illustration an example feedback MAC protocol dataunit (MPDU) format, according to an embodiment.

FIG. 3 is a diagram illustrating a control field, according to oneembodiment.

FIGS. 4A-4C are diagrams illustrating various feedback (FB) report fieldformats, in various embodiments and/or scenarios.

FIG. 5 is a flow diagram of an example method for transmitting channelestimate data from a receiver to a transmitter, according to anembodiment.

DETAILED DESCRIPTION

In embodiments described below, a wireless network device such as anaccess point (AP) of a wireless local area network (WLAN) transmits datastreams to one or more client stations. In some embodiments, WLANsupports multiple input multiple output (MIMO) communication in whichthe AP and/or the client stations include more than one antenna, therebycreating a plurality of spatial (or space-time) streams over which datacan be transmitted simultaneously. In an embodiment in which the APemploys multiple antennas for transmission, the AP utilizes variousantennas to transmit the same signal while phasing (and amplifying) thissignal as it is provided to the various transmit antennas to achievebeamforming or beamsteering. In order to implement a beamformingtechnique, the AP generally requires knowledge of certaincharacteristics of the communication channel between the AP and the oneor more client stations for which a beamforming pattern is to becreated. To obtain channel characteristics, according to one embodiment,the AP transmits to a client station a sounding packet including anumber of training fields that allow the client station to accuratelyestimate the MIMO channel. The client station then transmits or feedsback, in some form, the obtained channel characteristics to the AP, forexample by including channel characteristic information in a managementor a control frame transmitted to the AP. Upon receiving, from one ormore of the client stations, information characterizing thecorresponding communication channels, the AP is able to generate desiredbeam patterns to be used in subsequent transmissions to one or morestations.

FIG. 1 is a block diagram of an example wireless local area network(WLAN) 10 in which channel data feedback is utilized, according to anembodiment. The WLAN 10 supports downlink (DL) multiuser (MU)multiple-input and multiple-output (MIMO) communication between an AP 14and a plurality of client stations 25-i. Additionally, the WLAN 10supports DL single-user (SU) communication between the AP 14 and each ofthe client stations 25-i. The AP 14 includes a host processor 15 coupledto a network interface 16. The network interface 16 includes a mediumaccess control (MAC) processing unit 18 and a physical layer (PHY)processing unit 20. The PHY processing unit 20 includes a plurality oftransceivers 21, and the transceivers 21 are coupled to a plurality ofantennas 24. Although three transceivers 21 and three antennas 24 areillustrated in FIG. 1, the AP 14 can include different numbers (e.g., 1,2, 4, 5, etc.) of transceivers 21 and antennas 24 in other embodiments.In an embodiment, if the AP 14 performs beamforming or beam steering,and/or if the AP 14 operates in multiuser mode, the AP 14 includes atleast two antennas 24. The WLAN 10 includes a plurality of clientstations 25. Although four client stations 25 are illustrated in FIG. 1,the WLAN 10 can include different numbers (e.g., 1, 2, 3, 5, 6, etc.) ofclient stations 25 in various scenarios and embodiments. At least one ofthe client stations 25 (e.g., client station 25-1) is configured tooperate at least according to the first communication protocol.

The client station 25-1 includes a host processor 26 coupled to anetwork interface 27. The network interface 27 includes a MAC processingunit 28 and a PHY processing unit 29. The PHY processing unit 29includes a plurality of transceivers 30, and the transceivers 30 arecoupled to a plurality of antennas 34. Although three transceivers 30and three antennas 34 are illustrated in FIG. 1, the client station 25-1can include different numbers (e.g., 1, 2, 4, 5, etc.) of transceivers30 and antennas 34 in other embodiments. In an embodiment, if the clientstation 25-1 performs beamforming or beam steering, the client station25-1 includes at least two antennas 34.

In an embodiment, one or all of the client stations 25-2, 25-3 and 25-4has a structure the same as or similar to the client station 25-1. Inthese embodiments, the client stations 25 structured the same as orsimilar to the client station 25-1 have the same or a different numberof transceivers and antennas. For example, the client station 25-2 hasonly two transceivers and two antennas, according to an embodiment.

In various embodiments, the PHY processing unit 20 of the AP 14 isconfigured to generate data units conforming to the first communicationprotocol. The transceiver(s) 21 is/are configured to transmit thegenerated data units via the antenna(s) 24. Similarly, thetransceiver(s) 24 is/are configured to receive the data units via theantenna(s) 24. The PHY processing unit 20 of the AP 14 is configured toprocess received data units conforming to the first communicationprotocol, according to an embodiment.

In various embodiments, the PHY processing unit 29 of the client device25-1 is configured to generate data units conforming to the firstcommunication protocol. The transceiver(s) 30 is/are configured totransmit the generated data units via the antenna(s) 34. Similarly, thetransceiver(s) 30 is/are configured to receive data units via theantenna(s) 34. The PHY processing unit 29 of the client device 25-1 isconfigured to process received data units conforming to the firstcommunication protocol, according to an embodiment.

With continued reference to FIG. 1, according to one embodiment, aclient station, such as the client station 25-1, acquires in some manner(e.g., by receiving a sounding frame from the AP 14) characteristics ofthe channel between the AP 14 and the client station and feeds thisinformation back to the AP 14. Generally, such feedback informationtakes on one of a variety of forms in various embodiments and/orscenarios. According to one embodiment, for example, channel informationis sent in a compressed form (the compressed form is sometimes alsoreferred to as compressed beamforming feedback, or compressed Vfeedback). In this embodiment, feedback information comprises a set ofangles characterizing the channel. In an embodiment, feedbackinformation is the transmitted from a beamformee (e.g., client station25-1) to a beamformer (e.g., AP 14) to allow the beamformer to steersubsequent transmissions in the direction of the beamformee. Compressedfeedback configuration, in accordance with some embodiments of thepresent disclosure, is described in U.S. patent application Ser. No.13/161,209, entitled “Alternative Feedback Types For Downlink MultipleUser MIMO Configurations”, filed on Jun. 15, 2011, which is herebyincorporated by reference herein in its entirety.

In one embodiment, in a single user case, the client station 25-1 is thebeamformee, or the device to which beamforming is directed, and the AP14 is the beamformer, or the device performing beamforming orbeamsteering. In another embodiment, in a multiuser case, the AP 14performs beamforming simultaneously to a plurality of client stations25. In this embodiment, each client station 25 to which beamforming isdirected is a beamformee, and the AP 14 is the beamformer. In yetanother embodiment, the AP 14 is the beamformee and the client station25-1 is the beamformer.

FIG. 2 is a diagram illustration an example feedback MAC protocol dataunit (MPDU) 200, according to an embodiment. With reference to FIG. 1,in an embodiment, the client station 25-1 transmits the MPDU 200 to theAP 14 in order to communicate compressed beamforming channel informationto the AP 14. The MPDU 200 includes a category field 202 to indicate theparticular communication protocol being utilized. For example, in oneembodiment, the category field indicates that the VHT protocol is beingutilized. The MPDU 200 also includes an action field 204 to indicate thetype, or the format, of the channel feedback information included in theframe (e.g., compressed beamforming). The MPDU 200 further includes aVHT MIMO control field 206 and a compressed beamforming report field208, each of which is described in more detail below.

FIG. 3 is a diagram illustrating a control field 300, such as the VHTMIMO control field 206 of the MPDU 200 (FIG. 2), according to anembodiment. In one embodiment, the MPDU 200 includes the control field300 when WLAN 10 operates in a single user mode, i.e., when the AP 14transmits to only one of the client stations 25-i at a time. In anotherembodiment, the MPDU 200 includes the control field 300 when WLAN 10operates in a multiuser mode, i.e., when the AP 14 transmits (andbeamforms) to more than one of the client stations 25-i simultaneously.The control field 300 includes certain elements, or subfields, common toboth modes, while certain other elements or subfields are different forthe two modes.

The control field 300 includes an MU subfield 302 to indicate whether asingle user or a multiuser mode is being utilized (“a mode indicator”).In an example embodiment, the MU subfield 302 is set to a logic “0” toindicate single user feedback (SU FB), and is set to a logic “1” toindicate multiuser feedback “MU FB.” Alternatively, in anotherembodiment, a logic “0” indicates MU FB and a logic “1” indicates SU FB.

The control field 300 also includes an Nc subfield 304 and an Nrsubfield 306 to indicate a number or columns and a number of rows,respectively, in a steering matrix corresponding to the feedbackcommunication channel (i.e., the communication channel between thebeamformer and the beamformee). More specifically, in an embodiment, asteering matrix has dimensions corresponding to (number of transmitantennas)×(number of spatial (or space-time) streams) forming a steeringmatrix suitable for the communication channel to which the channelfeedback corresponds. Accordingly, in this embodiment, the Nc subfield304 indicates the number of spatial streams (or space-time streams ifspace-time encoding is utilized) corresponding to the communicationchannel, and the Nr subfield 306 indicates the number of transmitantennas used at the beamformer for steering transmissions to thebeamformee. In an embodiment, the particular number ofspatial/space-time streams to which the steering matrix corresponds isdetermined at the beamformee. As an example, in an embodiment, a maximumof eight transmit antennas and a maximum of eight receive antennas areutilized, forming a maximum of eight spatial/space-time streams. In thisembodiment, depending on the particular channel configuration to whichthe feedback corresponds, the Nc subfield 304 and the Nr subfield 306each contains a value in the range of 0 to 7 to indicate a correspondingnumber of spatial/space-time streams and a corresponding number oftransmit antennas, respectively. In other embodiments, other suitablechannel configurations are supported, and, accordingly, the Nc subfield304 and/or the Nr subfield 306 contain other suitable values in at leastsome situations.

The control field 300 also includes BW subfield 308 to indicate thechannel bandwidth to which the feedback data corresponds. In oneembodiment, the bandwidth subfield 308 includes two bits that are set tothe value of 0 to indicate a 20 MHz BW, the value of 1 to indicate a 40MHz BW, the value of 2 indicate an 80 MHz, and the value of 3 toindicate a 160 MHz BW. In other embodiments, the BW subfield 308includes other suitable number of bits and/or is used to indicate othersuitable bandwidths. The control field 300 also includes Ng subfield 310to indicate a tone grouping used to transmit the channel feedback, asdescribed in more detail below.

The codebook info subfield 312 indicates the number of bits used toquantize and/or encode the angles corresponding to the compressedfeedback. In an embodiment, a codebook is composed of entries of from(x, y), where the x value corresponds to the number of bits used toquantize the φ angle value, and the y value corresponds to the number ofbits used to quantize the ψ angle value. In an embodiment, the specificcodebook information depends on whether the SU or the MU mode is beingutilized. Accordingly, in this embodiment, the value of the subfield 312is interpreted differently for the two modes. In one embodiment, thesubfield 312 includes one bit allowing indication of one of two suitablecodebook entries. In an example embodiment utilizing two bits, a logic“0” indicates (2, 4) quantizing bits in SU mode (e.g., indicated by avalue of 0 in MU subfield 302), and (6, 8) quantizing bits in MU mode((e.g., indicated by a value of 1 in MU subfield 302). Similarly, in anembodiment, a logic “1” in subfield 312 indicates (4, 6) quantizing bitsin SU mode and (7, 9) quantizing bits in MU mode. Alternatively, inanother embodiment, the codebook info subfield 312 includes two bitsallowing indication of one of four suitable codebook entries, which areinterpreted differently for the SU and the MU modes. In one suchembodiment, for example, if SU mode is indicated (e.g., in the MUsubfield 302), a value of 0 is the codebook info subfield 312corresponds to a codebook entry of (1, 3), a value of 1 corresponds to acodebook entry of (2, 4), a value of 2 corresponds to a codebook entryof (3, 5), and a value of 2 corresponds to (4, 6). On the other hand, ifMU mode is indicated, in this example embodiment, a value of 0 is thecodebook info subfield 312 corresponds to a codebook entry of (4, 6), avalue of 1 corresponds to a codebook entry of (5, 7), a value of 2corresponds to a codebook entry of (6, 8), and a value of 2 correspondsto (7, 9).

Additionally, the control field 300 includes a sounding sequence numbersubfield 314 and a reserved subfield 316. In one embodiment, thereserved subfield 316 includes a number of bits needed to extend thecontrol field 300 to entirely cover 3 bytes. In another embodiment, thereserved subfield 316 includes a number of bits needed to extend thecontrol field 300 to entirely cover 4 bytes. In other embodiments, thereserved subfield 314 includes another suitable number of bits. Further,in an embodiment in which tone augmentation is used (e.g., in MU mode),one or more bits in the reserved subfield 316 are used to indicate toneaugmentation (e.g., one bit is used to indicate is tone augmentation isbeing utilized).

A feedback report field follows the control field and includes channelinformation corresponding to the communication channel between thebeamformer and the beamformee. In some embodiments, such as embodimentsutilizing multiple input, multiple output (MIMO) channels and/ororthogonal frequency division multiplexing (OFDM), the amount of channeldata fully characterizing the communication channel (“a full channelestimate”) is large. In embodiments utilizing multiple transmit andreceive antennas (i.e., MIMO channels), for example, a full channelestimate includes estimates of the sub-channels corresponding to eachtransmit and receive antenna pair. Further, in embodiments utilizingorthogonal frequency division multiplexing (OFDM), a full channelestimate includes channel estimates at each of the subcarrierfrequencies. Therefore, to reduce the amount of channel estimate datatransmitted from a beamformee (e.g., client station 25-1) to abeamformer (e.g., AP 14) in some embodiments, the beamformee transmitsonly a subset of the full channel estimate data. For example, in someembodiments utilizing OFDM-based communication, a technique ofsubcarrier grouping is utilized in which the OFDM subcarriers arecombined into groups, and channel estimate data corresponding to onlyone subcarrier in each group is transmitted back to the AP. Additionallyor alternatively, in some embodiments utilizing a subcarrier groupingtechnique, an average of channel estimate data corresponding to thesubcarriers in a group of subcarriers is transmitted back to the AP.

For example, in an embodiment, if the feedback channel data correspondsto a 20 MHz channel (with 52 OFDM data/pilot tones), feedback reportincludes channel data for all 52 tones if a tone grouping of 1 tone(i.e., no grouping) is being utilized, channel data for 30 OFDM tones ifa tone grouping of 2 tones is being utilized, and channel data for 16OFDM tones if a tone grouping of 4 is being utilized. In a 40 MHzchannel case (with 108 OFDM data/pilot tones), according to anembodiment, feedback report includes channel data for all 108 tones if atone grouping of 1 tone (i.e., no grouping) is being utilized, channeldata for 58 OFDM tones if a tone grouping of 2 tones is being utilized,and channel data for 30 OFDM tones if a tone grouping of 4 is beingutilized. Similarly, in an 80 MHz channel case (with 234 OFDM data/pilottones), according to an embodiment, feedback report includes channeldata for all 234 tones if a tone grouping of 1 tone (i.e., no grouping)is being utilized, channel data for 122 OFDM tones if a tone grouping of2 tones is being utilized, and channel data for 62 OFDM tones if a tonegrouping of 4 is being utilized. In an embodiment in which feedbackreport includes channel data for a 160 MHz channel, the feedback reportincludes channel data corresponding to 80 MHz subbands, with thecorresponding 80 MHz channel tone groupings described above. A moredetailed description of various tone groupings and some specificexamples of feedback tones, according to some embodiments of the presentdisclosure, is found in U.S. patent application Ser. No. 13/207,003,entitled “Channel Description Feedback in a Communication System”, filedon Aug. 10, 2011, which is hereby incorporated by reference herein inits entirety. In an embodiment, the particular subcarrier grouping beingutilized is indicated in the Ng subfield 310 of the control field 300(FIG. 3).

In some embodiments, a 40 MHz, an 80 MHz or a 160 MHz channel is formedof a primary 20 MHz channel and a number of subband extension channels,the particular number or subband channels depending on the bandwidthbeing utilized. In some such embodiments, a feedback report for a 40MHz, a 80 MHz, or a 160 Mhz channel includes data corresponding to onlya portion of the entire channel. For example, a feedback report for a 40MHz channel, includes feedback data for a 20 MHz subchannel, accordingto an embodiment. Similarly, a feedback report for a 80 MHz channelincludes feedback data for a 20 MHz subchannel, in an embodiment. Inanother embodiment, a feedback report for a 80 MHz channel includesfeedback data for a 40 MHz subchannel. In some such embodiments, thebeamformer, upon receiving the feedback data, interprets the feedback ascorresponding to the primary 20 MHz channel. Further, if the feedbackdata corresponds to a larger bandwidths the 20 MHz primary channel, suchas a 40 MHz BW or an 80 MHz BW, the beamformer interprets the feedbackdata as corresponding to a channel subband containing the primary 20 MHzchannel. Primary and extension subband channels, in accordance with someembodiments of the present disclosure, are described in U.S. patentapplication Ser. No. 13/205,257, entitled “Sub-Band Feedback ForBeamforming on Downlink Multiple User MIMO Configurations”, filed onAug. 8, 2011, which is hereby incorporated by reference herein in itsentirety.

FIGS. 4A-4C are diagrams illustrating various feedback (FB) report fieldformats included in the MPDU 200 (e.g., compressed beamforming reportfield 208 in FIG. 2) for SU and/or MU modes, in various embodimentsand/or scenarios. Referring to FIG. 4A, in an embodiment, FB reportfield 400 is used for a single user case. The FB report field 400includes a plurality of Avg-SNR subfields 402 which include signal tonoise (SNR) values averaged over a plurality of OFDM tones for aplurality of spatial/space-time streams. Accordingly, in an embodiment,the number of Avg-SNR subfields 402 corresponds to the number ofspatial/space-time streams included in the feedback (i.e., the numberspatial/space-time streams for which channel information is fed back).The FB report field 400 also includes a plurality of angle subfields 404which include the quantized angle values as indicated, for example, inthe codebook information subfield 312 of the control field 300 (FIG. 3).In other words, the number of angle subfields 404 generally correspondsto the number of spatial/space-time streams, and each angle subfield 404includes quantized angle values for a number of OFDM tones(corresponding to feedback tones) associated with a particularspatial/space-time stream. For convenience, FIG. 4A explicitly showssubfields associated with only two OFDM feedback tones. However, invarious embodiments and/or scenarios, the FB report field 400 includesangle data for any suitable number of OFDM feedback tones.

Referring now to FIG. 4B, the FB report field 430 is used in a multiusercase, according to an embodiment. The FB report field is similar to FBreport filed 400, except that the FB report filed 430 also includes aplurality of “per-tone” signal to noise (PT-SNR) subfields generallyillustrated in FIG. 4B at blocks 434 and blocks 438. That is, in theembodiment illustrated in FIG. 4B, in a multiuser case, the FB reportfield includes a PT SNR value for to each feedback tone, in addition tothe average SNR over a plurality of OFDM tones. More specifically, in anembodiment, PT-SNR subfields 434 include SNR values associated with afirst OFDM feedback tone for each of the spatial/space-time streamincluded in the feedback. Similarly, PT-SNR subfields 438 include SNRvalues associated with a second OFDM feedback tone for each of thespatial/space-time stream included in the feedback. For convenience,FIG. 4B explicitly shows subfields associated with only two OFDMfeedback tones. However, in various embodiments and/or scenarios, the FBreport field 430 includes angle data and per-tone SNR data for anysuitable number of OFDM feedback tones.

FIG. 4C illustrates another FB feedback report 460 which includesper-tone SNR values, according to another embodiment. The FB feedbackreport 460 is used in a multiuser case, according to an embodiment. TheFB feedback report field 460 is similar to the FB report field 430,except that in the FB report field 460, a plurality of PT-SNR subfields466, a plurality of PT-SNR subfields 468, etc. are included after theangle subfields 464. In general, PT-SNR subfields are included at anysuitable locations within an FB report field, in various embodimentsand/or scenarios.

In the embodiments described above, per-tone SNR values are included ina multiuser mode, while only the avg-SNR values are included in a singleuser mode. In these embodiments, average SNRs provide sufficientinformation to effectively perform beamforming in a single user case,while additional (per-tone) SNR data is beneficial to for a multiusercase. In some embodiments, however, a FB report field includes per-toneSNR values, in addition to the avg-SNR values, for a single user case aswell as for a multiuser case.

In an embodiment, the average SNR values (e.g., included in the avg-SNRsubfields 402, the avg-SNR subfields 432, and/or the avg-SNR subfields462) are quantized using an eight bit two's compliment integer of4×(SNR_(AVG) _(—) _(i)−22), wherein SNR_(AVG) _(—) _(i) is the averageSNR corresponding to the i^(th) spatial/space-time stream. In thisembodiment, a quantized avg-SNR value for each spatial/space-time streamis within the range of −10 dB to 53.75 dB, in 0.25 dB steps. Similarly,in an embodiment, each of the PT-SNR values (e.g., included in thePT-SNR subfields 434, the PT-SNR subfields 438, the PT-SNR subfields466, and/or the PT-SNR subfields 468) is quantized to eight bits usingan eight bit two's compliment integer of 4×(SNR_(i)−22), wherein SNR isthe SNR corresponding to the respective OFDM tone for the i^(th)spatial/space-time stream. In another embodiment, each of the PT-SNRvalues is quantized to four bits using a four bit two's complimentinteger of (SNR_(i)−22), wherein SNR is the SNR corresponding to therespective OFDM tone for the i^(th) spatial/space-time stream. In thiscase, the quantized PT-SNRs are in the range of −10 dB to 50 dB in 4 dBsteps.

Alternatively, in some embodiments, a delta between per-tone SNR and theaverage SNR for a group of tones for the correspondingspatial/space-time stream is quantized and the quantized delta value isincluded in a corresponding PT-SNR subfield. For example, in one suchembodiment, the quantized delta corresponds to a four bit two'scomplement integer of (SNR_(i)−SNR_(AVG) _(—) _(i))/2, wherein SNR_(i)is the SNR corresponding to the respective OFDM tone for the i^(th)spatial/space-time stream, and SNR_(AVG) _(—) _(i) is the average SNRfor the corresponding spatial/space-time stream. In this embodiment, thequantized per-tone SNR delta is in the range of −16 dB to 14 dB, in 2 dBsteps. As another example, in another embodiment, the quantized deltacorresponds to a four bit two's complement integer of (SNR_(i)−SNR_(AVG)_(—) _(i)), wherein SNR_(i) is the SNR corresponding to the respectiveOFDM tone for the i^(th) spatial/space-time stream, and SNR_(AVG) _(—)_(i) is the average SNR for the corresponding spatial/space-time stream.In this embodiment, the per-tone SNR delta is in the range of −8 dB to 7dB in 1 dB steps. Other suitable quantization techniques are used togenerate quantized values representing per-tone SNR values in otherembodiments.

Referring back to FIG. 2, in some embodiments, the MPDU 200 is includedin a feedback Action-No-Action frame of action type +HTC (or a “+HTCframe”), which also includes feedback corresponding to a modulation andcoding scheme (MCS) selected at the beamformee and sent back to thebeamformer. In some such embodiments, the number of columns Nc (e.g.,included in the Nc subfield 304 of FIG. 3) is the same as the number ofspatial/space-time streams (Nss) corresponding to the feedback MCS.

According to an embodiment, when a beamformer (e.g., the AP 14) receivesthe feedback MPDU 200, in a single user case, the beamformer interpretsthe Nc value (e.g., indicated by the Nc subfield 304 of FIG. 3) as thebest number of spatial/space-time streams recommended by the beamformeeto be used for beamforming to the beamformee. On the other hand, in amultiuser case, when a beamformer (e.g., the AP 14) receives thefeedback MPDU 200, the beamformer interprets the Nc value (e.g.,indicated by the Nc subfield 304 of FIG. 3) as the maximum number ofspatial/space-time streams to be used for beamforming in the directionof the beamformee. In this embodiment, the beamformer determines theactual number of spatial/space-time streams to be used for thebeamformee based on feedback received from all of the users to whichbeamforming is to be simultaneously performed. In this embodiment, abeamsteering matrix for all of the users is jointly calculated, takinginto account feedback information received from all of the correspondingusers (to which the particular transmission is being steered).

FIG. 5 is a flow diagram of an example method 500 for transmittingchannel estimate data from a receiver to a transmitter, according to anembodiment. With reference to FIG. 1, the method 500 is implemented bythe network interface 27 of the client station 25-1, in an embodiment.For example, in one such embodiment, the PHY processing unit 29 isconfigured to implement the method 500. According to another embodiment,the MAC processing 28 is also configured to implement at least a part ofthe method 500. With continued reference to FIG. 1, in yet anotherembodiment, the method 500 is implemented by the network interface 16(e.g., the PHY processing unit 20 and/or the MAC processing unit 18). Inother embodiments, the method 500 is implemented by other suitablenetwork interfaces.

At block 502, channel data for a plurality of OFDM tones for one or morespatial/space-time streams corresponding to the communication channel(e.g., the channel between the AP 14 and the client station 25-1) isdetermined. In an embodiment, channel data is determined based on one ormore training fields included in a sounding wave that the receiverreceives from the transmitter. At block 504, a compressed form of thechannel data determined at block 502 is generated. In an embodiment,generating compressed form of the channel data comprises generating aplurality of angels associated with the communication channel for acorresponding number of spatial/space-time streams and the plurality ofOFDM tones. Referring to FIGS. 4A-4C, in one embodiment, the anglevalues determined at block 504 correspond to the values included in theangle subfields 404 of FIG. 4A, the angle subfields 436 and 440 of FIG.4B, or the angle subfields 464 of FIG. 4C.

At block 506, per-tone SNR (PT-SNR) is generated for one or more of theplurality of OFDM tones. In an embodiment, the PT-SNR values determinedat block 506 correspond to the PT-SNR subfields 434 and 438 of FIG. 4B,or the PT-SNR subfields 466 and 468 of FIG. 4C. At block 508, averageSNR (avg-SNR) over a group of OFDM tones is determined for eachspatial/space-time stream. In an embodiment, the avg-SNR valuesdetermined at block 506 correspond to the avg-SNR subfields 402 of FIG.4A, the avg-SNR subfields 432 of FIG. 4B, or the avg-SNR subfields 462of FIG. 4C are determined at block 508.

At block 510, a data unit is generated to include at least i) theplurality of angle values corresponding to the one or morespatial/space-time streams and the one or more OFDM tones, ii) thePT-SNRs corresponding to the one or more spatial/space-time streams andthe one or more OFDM tones, and iii) the avg-SNR corresponding to theone or more spatial/space-time streams. In one embodiment, generatingthe data unit at block 510 includes quantizing the angle values usingthe number of bits indicated in the codebook information subfield 312 ofFIG. 3. In an embodiment, generating the data unit at block 510 alsoincludes quantizing the PT-SNR values and the avg-SNR values asdiscussed above. As also discussed above, in one embodiment, the PT-SNRvalues are omitted in a single user case (i.e., when the feedback reportis to be used for steering to a single user).

At block 512, the feedback report generated at block 510 is included ina data unit to be transmitted from a receiver (a beamformee) to atransmitter (a beamformer).

At least some of the various blocks, operations, and techniquesdescribed above may be implemented utilizing hardware, a processorexecuting firmware instructions, a processor executing softwareinstructions, or any combination thereof. When implemented utilizing aprocessor executing software or firmware instructions, the software orfirmware instructions may be stored in any computer readable memory suchas on a magnetic disk, an optical disk, or other storage medium, in aRAM or ROM or flash memory, processor, hard disk drive, optical diskdrive, tape drive, etc. Likewise, the software or firmware instructionsmay be delivered to a user or a system via any known or desired deliverymethod including, for example, on a computer readable disk or othertransportable computer storage mechanism or via communication media.Communication media typically embodies computer readable instructions,data structures, program modules or other data in a modulated datasignal such as a carrier wave or other transport mechanism. The term“modulated data signal” means a signal that has one or more of itscharacteristics set or changed in such a manner as to encode informationin the signal. By way of example, and not limitation, communicationmedia includes wired media such as a wired network or direct-wiredconnection, and wireless media such as acoustic, radio frequency,infrared and other wireless media. Thus, the software or firmwareinstructions may be delivered to a user or a system via a communicationchannel such as a telephone line, a DSL line, a cable television line, afiber optics line, a wireless communication channel, the Internet, etc.(which are viewed as being the same as or interchangeable with providingsuch software via a transportable storage medium). The software orfirmware instructions may include machine readable instructions that,when executed by the processor, cause the processor to perform variousacts.

When implemented in hardware, the hardware may comprise one or more ofdiscrete components, an integrated circuit, an application-specificintegrated circuit (ASIC), a programmable logic device (PLD), etc.

While the present invention has been described with reference tospecific examples, which are intended to be illustrative only and not tobe limiting of the invention, changes, additions and/or deletions may bemade to the disclosed embodiments without departing from the scope ofthe invention.

What is claimed:
 1. A method for transmitting channel feedback data froma receiver to a transmitter, the method comprising: determining channeldata for a plurality of orthogonal frequency division multiplexing(OFDM) tones of one or more spatial or space-time streams correspondingto a communication channel; determining a compressed form of the channeldata including determining a plurality of angle values associated withi) the one or more spatial or space-time streams and ii) one or moreOFDM tones of the plurality of OFDM tones; for each of the one or morespatial or space-time streams: i) determining an average signal to noiseratio (avg-SNR) by averaging signal to noise ratio (SNR) valuescorresponding to one or more OFDM tones of the plurality of OFDM tones,and ii) determining a per-tone signal to noise ratio (PT-SNR) associatedwith one or more OFDM tones of the plurality of OFDM tones, generating afeedback report to include at least i) the plurality of angle valuesassociated with the one or more spatial or space-time streams and theone or more OFDM tones, ii) deltas corresponding to the PT-SNRsassociated with the one or more spatial or space-time streams and the atleast some of the one or more OFDM tones, wherein each delta correspondsto a difference between the respective PT-SNR and the avg-SNR associatedwith the one or more spatial or space-time streams, and iii) the avg-SNRassociated with the one or more spatial or space-time streams; andincluding the feedback report in a data unit to be transmitted from thereceiver to the transmitter.
 2. A method according to claim 1, whereinthe data unit also includes a control field, wherein the control fieldincludes at least i) a mode indicator to indicate if the channel datawill be used in single user (SU) mode or in multiuser (MU) mode, ii) anumber of columns (Nc) indicator to indicate a number of columns in achannel matrix corresponding to the communication channel, and iii)codebook information to indicate a number of bits used for quantizingeach angle value of the plurality of angle values.
 3. A method accordingto claim 2, wherein the deltas are omitted from the feedback report whenthe mode indicator is set to indicate SU mode.
 4. A method according toclaim 2, wherein codebook information is interpreted differently for theSU and the MU modes.
 5. A method according to claim 2, wherein codebookinformation is indicated using one bit.
 6. A method according to claim1, wherein generating the feedback report includes quantizing theavg-SNR values to generate eight bit quantized avg-SNRs.
 7. A methodaccording to claim 1, wherein generating the feedback report includesquantizing the deltas to generate four bit quantized deltas.
 8. A methodaccording to claim 2, wherein the data unit further includes amodulation and coding scheme (MCS) feedback indicator, and wherein Nc isequal to the number of spatial or space-time streams corresponding tothe MCS feedback indicator.
 9. A method according to claim 1, whereinthe feedback report includes angle values and deltas corresponding toonly one OFDM tone in each group of a number of OFDM tones.
 10. A methodaccording to claim 2, wherein Nc indicates the best number of spatial orspace-time streams to be used for beamforming to the receiver when themode indicator is set to indicate SU mode, and wherein Nc indicates themaximum number of spatial or space-time streams to be used forbeamforming to the receiver when the mode indicator is set to indicateMU mode.
 11. An apparatus comprising: a network interface configured to:determine channel data for a plurality of orthogonal frequency divisionmultiplexing (OFDM) tones of each of one or more spatial or space-timestreams corresponding to a communication channel; determine a compressedform of the channel data including determining a plurality of anglevalues associated with i) the one or more spatial or space-time streams,and ii) one or more OFDM tone of the plurality of OFDM tones; for eachof the one or more spatial or space-time streams: i) determine anaverage signal to noise ratio (avg-SNR) by averaging signal to noiseratio (SNR) values corresponding to one or more OFDM tones of theplurality of OFDM tones, and ii) determine a per-tone signal to noiseratio (PT-SNR) associated with one or more OFDM tones of the pluralityof OFDM tones, wherein the PT-SNR is represented by a delta between thePT-SNR for the corresponding tone and the avg-SNR; and generate afeedback report to include at least i) the plurality of angle valuesassociated with the one or more spatial or space-time streams and theone or more OFDM tones, ii) deltas corresponding to the PT-SNRsassociated with the one or more spatial or space-time streams and the atleast some of the one or more OFDM tones, wherein each delta correspondsto a difference between the respective PT-SNR and the avg-SNR associatedwith the one or more spatial or space-time streams, and iii) the avg-SNRassociated with the one or more spatial or space-time streams; andinclude the feedback report in a data unit to be transmitted for thereceiver to the transmitter.
 12. An apparatus according to claim 10,wherein the data unit includes a control field, wherein the controlfield includes at least i) a mode indicator to indicate if the channeldata will be used in single user (SU) mode or in multiuser (MU) mode,ii) a number of columns (Nc) indicator to indicate a number of columnsin a channel matrix corresponding to the communication channel, and iii)codebook information to indicate a number of bits used for quantizingeach angle value of the plurality of angle values.
 13. An apparatusaccording to claim 12, wherein the network interface is configured toomit the deltas from the feedback report when the mode indicator is setto indicate SU mode.
 14. An apparatus according to claim 12, whereincodebook information is interpreted differently for the SU and the MUmodes.
 15. An apparatus according to claim 12, wherein codebookinformation is indicated using one bit.
 16. An apparatus according toclaim 11, wherein generating the feedback report includes quantizing theavg-SNR values to generate eight bit quantized avg-SNRs.
 17. Anapparatus according to claim 11, wherein generating the feedback reportincludes quantizing the deltas to generate four bit quantized deltas.18. An apparatus according to claim 12, wherein the data unit furtherincludes a modulation and coding scheme (MCS) feedback indicator, andwherein Nc is equal to the number of spatial or space-time streamscorresponding to the MCS feedback indicator.
 19. An apparatus accordingto claim 11, wherein the feedback report includes angle values anddeltas corresponding to only one OFDM tone in each group of a number ofOFDM tones.
 20. An apparatus according to claim 12, wherein Nc indicatesthe best number of spatial or space-time streams to be used forbeamforming to the receiver when the mode indicator is set to indicateSU mode, and wherein Nc indicates the maximum number of spatial orspace-time streams to be used for beamforming to the receiver when themode indicator is set to indicate MU mode.